1. Field of the Invention
The present disclosure generally relates to apparatus and methods for sealing in offshore wellbores. More particularly, the present disclosure relates to apparatus and methods to seal against a drill pipe in subsea wellbores offshore during drilling operations.
2. Background Art
Wellbores are drilled deep into the earth's crust to recover oil and gas deposits trapped in the formations below. Typically, these wellbores are drilled by an apparatus that rotates a drill bit at the end of a long string of threaded pipes known as a drillstring. Because of the energy and friction involved in drilling a wellbore in the earth's formation, drilling fluids, commonly referred to as drilling mud, are used to lubricate and cool the drill bit as it cuts the rock formations below. Furthermore, in addition to cooling and lubricating the drill bit, drilling mud also performs the secondary and tertiary functions of removing the drill cuttings from the bottom of the wellbore and applying a hydrostatic column of pressure to the drilled wellbore.
As wellbores are drilled several thousand feet below the surface, the hydrostatic column of drilling mud serves to help prevent blowout of the wellbore as well. Often, hydrocarbons and other fluids trapped in subterranean formations exist under significant pressures. Absent any flow control schemes, fluids from such ruptured formations may blow out of the wellbore like a geyser and spew hydrocarbons and other undesirable fluids (e.g., H2S gas) into the atmosphere. As such, several thousand feet of hydraulic “head” from the column of drilling mud helps prevent the wellbore from blowing out under normal conditions.
However, under certain circumstances, the drill bit will encounter pockets of pressurized formations and will cause the wellbore to “kick” or experience a rapid increase in pressure. Because formation kicks are unpredictable and would otherwise result in disaster, flow control devices known as blowout preventers (“BOPs”), are mandatory on most wells drilled today. One type of BOP is an annular blowout preventer. Annular BOPs are configured to seal the annular space between the drillstring and the inside of the wellbore. Annular BOPs typically include a large flexible rubber packing unit of a substantially toroidal shape that is configured to seal around a variety of drillstring sizes when activated by a piston. Furthermore, when no drillstring is present, annular BOPs may even be capable of sealing an open bore. While annular BOPs are configured to allow a drillstring to be removed (i.e., tripped out) or inserted (i.e., tripped in) therethrough while actuated, they are not configured to be actuated during drilling operations (i.e., while the drillstring is rotating). Because of their configuration, rotating the drillstring through an activated annular blowout preventer would rapidly wear out the packing element.
As such, rotating control devices are frequently used in oilfield drilling operations where elevated annular pressures are present. A typical rotating control device (RCD) includes a packing element and a bearing package, whereby the bearing package allows the packing element to rotate along with the drillstring. Therefore, in using a RCD, there is no relative rotational movement between the packing element and the drillstring, only the bearing package exhibits relative rotational movement. Examples of RCDs include U.S. Pat. No. 5,022,472 issued to Bailey et al. on Jun. 11, 1991 (assigned to Drilex Systems), and U.S. Pat. No. 6,354,385 issued to Ford et al. on Mar. 12, 2002, assigned to the assignee of the present application, and both are hereby incorporated by reference herein in their entirety. In some instances, dual stripper rotating control devices having two sealing elements, one of which is a primary seal and the other a backup seal, may be used. As the assembly of the bearing package along with the sealing elements and the drillstring rotate, leaks may occur between the drillstring and the primary sealing element. An apparatus or method of detecting and isolating leaks between the drillstring and sealing element while drilling would be well received in the industry.